Uncoupling of invasive bacterial mucosal immunogenicity from pathogenicity

Area of Science:

• Microbiology
• Immunology
• Gastroenterology

Background:

• Virulent intestinal pathogens often induce stronger mucosal adaptive immunity than avirulent strains.
• The role of inflammation in effective immunity induction remains unclear.

Purpose of the Study:

• To investigate if bacterial virulence factors can induce immunity independently of inflammation.
• To determine the role of innate pathogen sensing pathways in Salmonella immunity.
• To assess the impact of microbiota on Salmonella colonization and immunity.

Main Methods:

• Auxotrophic Salmonella infection model in germ-free mice.
• Assessment of innate immune signaling pathways (MYD88/TRIF, inflammasome, NOD1/NOD2).
• Analysis of microbiota metabolite cross-feeding and its effect on colonization and immunity.

Main Results:

• Live auxotrophic Salmonella induced protective mucosal immunity via virulence factors, without causing inflammation.
• Virulence factor-deficient or killed bacteria showed reduced immunogenicity.
• MYD88/TRIF, inflammasome, and NOD1/NOD2 signaling were individually redundant for immunity.
• Microbiota metabolite cross-feeding restored colonization but not pathogenicity.
• Immunoglobulin A (IgA) immunity and microbial niche competition synergistically protected against wild-type Salmonella.

Conclusions:

• Bacterial virulence factors are key drivers of protective mucosal immunity, separable from inflammatory pathogenicity.
• Innate immune sensing pathways are redundant, highlighting the importance of adaptive immunity.
• Microbiota and IgA play synergistic roles in conferring robust protection against enteric pathogens.